Cable with features for distinguishing between fiber groups

ABSTRACT

Micromodule subunit cables are constructed to allow for ease of identification between optical fibers in differing groups of optical fibers. In one cable, a first group of fibers is located within a buffer tube core while a second group of fibers is located within the cable jacket, but outside of the core. The fibers in the first and second groups can accordingly use the same color coding sequence without requiring additional indicia such as stripes or binding.

PRIORITY APPLICATION

This application is a continuation of U.S. application Ser. No.12/787,597 filed May 26, 2010, which claims priority to U.S. applicationSer. No. 61/219,929, filed Jun. 24, 2009, the entire contents of each ofwhich are hereby incorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates to optical cables with features thatprovide easy access to and segregation between optical fibers indifferent groups of optical fibers.

BACKGROUND

Data centers require high density for optical components to compensatefor limited space. MTP connectors are used in data centers because theyallow for high density, as well as high efficiency. 24 fiber MTPconnectors, for example, provide for high density optical connectivity.Typical MTP connectors are designed for a cable of circular profile andan outer diameter of 3.3 mm or less.

During cable access and connectorization of 24f cables, the installermust be able to distinguish fibers 1-12 in the first group of fibersfrom fibers 13-24 in the second group. There are, however, only twelvecolors used in the industry standard color coding scheme. One method todistinguish the two groups fibers is to provide fibers 13-24 withmarking indicia, such as dashed lines, to distinguish them from fibers1-12. Fiber coloring inks are applied and cured at extremely highspeeds, however, and applying dashes or other indicia slows productionline speed as well as increasing costs of manufacture.

Another method of distinguishing between fiber groups is to bundlefibers 13-24 in the second group with a thread binder that is wrappedaround the bundle of fibers. The binder can untwist, however, when theinstaller removes the outer jacket of the cable. When the binderuntwists, the installer loses traceability between the two groups of 12colored fibers.

Conventional cables may also be difficult to connect to MTP connectors,or have bend characteristics that render the cables difficult to routethrough data center space.

SUMMARY

According to a first embodiment, a cable comprises a cable jacket, acore located within the cable jacket and including a core tube with afirst group of optical fibers located therein, and a second group offibers located outside of the core tube. The first group of fibers arereadily distinguishable from the second group by their inclusion withinthe core tube so that traceability is retained during accessing of thecable.

According to one aspect of the first embodiment, the cable may havenon-preferential bend characteristics and may be easily connectorized.

According to another aspect of the first embodiment, a plurality of thecables may be incorporated into a micromodule cable. The cables may besufficiently robust so as to be suitable as furcation legs.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of the invention,and are intended to provide an overview or framework for understandingthe nature and character of the invention as it is claimed.

BRIEF DESCRIPTION OF THE FIGURES

The present embodiments are explained in more detail below withreference to figures which show the exemplary embodiments.

FIG. 1 is a cross section of a micromodule cable according to a firstembodiment.

FIG. 2 is a sectional view of one of the micromodule subunit cables usedin the cable of FIG. 1.

FIG. 3 is a sectional view of a micromodule subunit cable according to asecond embodiment.

DETAILED DESCRIPTION

FIG. 1 is a cross section of a micromodule cable 10 according to a firstembodiment and having an outside diameter 12. The micromodule cable 10comprises a plurality of micromodule subunit cables 20 disposed in aninterior 30 of the micromodule cable 10. The interior 30 of the cable 10is defined by the cable's outer jacket 50. The outer jacket 50 can beformed from, for example, a flame-retardant polymer material, and has athickness 52. A strain-relief component 56 may be disposed adjacent tothe interior of the jacket 50 and surrounding and/or interspersed amongthe micromodule cable subunits 20. The strain-relief component 56 maybe, for example, a layer of longitudinally-extending yarns for absorbingtensile loads on the cable 10. Each micromodule subunit cable, or simply“micromodule,” 20, includes a plurality of optical fiber waveguides 60.The exemplary micromodules 20 are not stranded within the cable 10,although stranding may be used for certain applications. For example,the micromodules 20 can be twisted in helical fashion with respect toone another, in particular when a plurality of or all of themicromodules 20 are arranged in such a way that they are rotated with aspecified lay length.

In the illustrated embodiment, the micromodule cable 10 has twelvemicromodule subunit cables 20, with each micromodule 20 including 24optical fiber waveguides 60. Other numbers of micromodule subunits 20and optical fibers 60 can be employed for various applications, however.The micromodule cable 10 and the micromodule subunit cables 20 all havegenerally circular cross-sections, although other cross-sections, suchas oval or elliptical, may be used. The diameters of the variouscircular cross-sections are described to in this specification. It isunderstood that the illustrated cables and subunits will not haveperfectly circular cross sections, and that any citations of diametersmay represent an average diameter of a generally circular cross section.

FIG. 2 is a cross section of one of the exemplary micromodule subunitcables 20 illustrated in FIG. 1 having a diameter 22. Each micromodulesubunit 20 has a cable jacket 70 of thickness 72 that encloses a core100. A strain-relief component 104 may be disposed within an interior106 of the cable jacket 70 and surrounding the core 100. Thestrain-relief component 104 may be, for example, a layer oflongitudinally-extending yarn strands that extend along the length ofthe micromodule subunit cable 20 for absorbing tensile loads on thecable. The exemplary strain-relief component 104 essentially comprises adispersed layer of aramid strands in the region between the jacket 70and the core 100, and is not illustrated schematically in FIG. 2.Instead, the general location of the strain-relief component 104 isindicated.

According to one aspect of the first embodiment, the optical fibers 60are arranged in a first group 110 that are located within a core tube114 of the core 100, and in a second group 120 that is located outsideof the core 100. The optical fibers 60 within the first group 110, whichare enclosed within the core tube 114, are accordingly segregated andeasily distinguishable from those in the second group 120. The featureensures that the installer retains traceability between the two groupsof 12 colored fibers.

According to the disclosed embodiment, each of the optical fibers 60 inthe first group 110 may have a corresponding optical fiber 60 in thesecond group 120 that is identical in appearance and/or color. The terms“identical” or “the same” allow for minor manufacturing variations amongthe similarly-colored fibers. In the context of this specification, astatement that one fiber has the same color and appearance as anotherfiber means that neither fiber of a certain color in one group has orrequires additional identifying indicia (e.g. stripes) applied todistinguish it from the same colored fiber in another group. There is noneed to provide identifying indicia on the optical fibers 60 of eitherof the groups 110, 120 in order to distinguish between the groupsbecause the first group 110 is enclosed within the core tube 114. Alsoaccording to the disclosed embodiment, there is no need to enclose onefiber group in a thread binder, or to enclose both groups of fiberswithin separate, individually marked buffer tubes, in order todistinguish between the fibers of each group.

In one embodiment, the first group 110 includes twelve optical fibers 60in a 12 color sequence of blue, orange, green, brown, slate, white, red,black, yellow, purple, rose, and aqua. The second group 120 alsoincludes twelve optical fibers in a 12 color sequence of blue, orange,green, brown, slate, white, red, black, yellow, purple, rose, and aqua.The fibers 60 of the first group 110 are therefore identical inappearance to the fibers in the second group 120. The technicianaccessing the fibers 60 within the cable 10 can nonetheless quickly andeasily distinguish the fibers 60 in the two groups because the firstgroup 110 is located within the core tube 114, which segregates thegroups 110, 120 during access and connectorization.

The optical fibers 60 in the second group 120 can be arranged in thejacket interior 106 around the core 100 and may be in contact with thestrands of the strain-relief component 104. For example, the secondgroup 120 of fibers can be arranged around the core 100, with thestrain-relief component 104 helically wrapped around the fiber in thesecond group 120 and the core 100. One or more of the optical fibers 60in the second group 120 are in at least intermittent contact with theexterior of the core tube 114.

The diameters and thicknesses of the micromodule subunit cable 20 and ofthe core tube 114 can vary according to the number of optical fibers 60enclosed therein, and according to other factors. According to oneaspect of the present embodiments, the diameter 22 can be in the rangeof 2.0 mm to 5.0 mm. According to another aspect of the presentembodiments, the diameter 22 can be in the range of 3.0 mm to 4.0 mm,and more particularly 3.5 mm or less. If the cable 20 is to be used toconnect to certain MTP connectors, the diameter can be 3.3 mm or less.According to another aspect of the present embodiments, the thickness 72of the cable jacket 70 can be in the range of 0.2 mm to 1.5 mm.According to one aspect of the present embodiments, the diameter of thecore tube 114 can be in the range of 0.9 mm to 3.0 mm According toanother aspect of the present embodiments, the diameter of the core tube114 can be in the range of 1.5 mm to 2.5 mm. According to another aspectof the present embodiments, the thickness of the core tube 114 can be inthe range of 0.1 mm to 0.95 mm.

EXAMPLE 1

A micromodule subunit cable 20 as shown in FIG. 2 includes a first group110 of twelve optical fiber waveguides 60 and a second group 120 oftwelve optical fiber waveguides 60. Each group 110, 120 includes fiberscoded in the 12-color sequence: blue, orange, green, brown, slate,white, red, black, yellow, purple, rose, and aqua. For each fiber 60 inthe first group 110, there is a corresponding fiber 60 in the secondgroup 120 of identical appearance, including color or external patternor identifying indicia, if any. In this example, the fibers in bothgroups are of solid color with no identifying indicia. The cablediameter 22 is about 3.3 mm, and the thickness 72 of the jacket 70 isabout 0.4 mm The diameter of the core 100 buffer tube 114 is about 1.6mm, and the thickness of the core tube 114 is about 0.2 mm. The fibers60 are bare, non-tight buffered fibers of about 0.250 mm diameter andare sold as ClearCurve® multimode fiber available from CorningIncorporated. The jacket 70 is made from a flame-retardant PVC soldunder the compound number 910A-18 available from Teknor Apex Co. Thecore tube 114 is made from a flame-retardant PVC sold under the compoundname Smokeguard™ 1070L available from AlphaGary Corporation. Thestrain-relief component 104 comprises KEVLAR® aramid tensile yarnsdisposed around the core 100. From 2-8 strands of tensile yarn are used.The subunit cable is connectorized to MTP connectors.

The present cable embodiments may utilize tensile yarns as tensionrelief elements that provide tensile strength to the cables. A preferredmaterial for the tensile yarns is aramid (e.g., KEVLAR®), but othertensile strength materials could be used. For example, high molecularweight polyethylenes such as SPECTRA® fiber and DYNEEMA® fiber, TeijinTwaron® aramids, fiberglass, etc. may also be used. The yarns may bestranded to improve cable performance.

The components of the cable 10, such as the micromodule cables 20, canbe constructed of selected materials of selected thicknesses such thatthe cable 10 achieves plenum burn ratings according to desiredspecifications. The micromodule subunit cables 20 can also beconstructed so that they are relatively robust, such that they aresuitable for field use, while also providing a desired degree ofaccessibility. For example, the micromodule cables 20 according to thepresent embodiment can be constructed with thicker cable jackets 70which provide sufficient protection for the fibers such that themicromodules 20 may be used as furcation legs.

The outer jacket 50, the micromodule subunit jackets 70, and the coretubes 114 can be formed from fire-retardant materials to obtain adesired plenum burn rating. For example, highly-filled PVCs of aspecified thicknesses can be used to form these components. Othersuitable materials include low smoke zero halogen (LSZH) materials suchas flame retardant polyethylene and PVDF. One plenum burn standard isthe National Fire Protection Standards (NFPA) 262 burn test. NFPA 262prescribes the methodology to measure flame travel distance and opticaldensity of smoke for insulated, jacketed, or both, electrical wires andcables and optical fiber cables that are to be installed in plenums andother spaces used to transport environmental air without being enclosedin raceways. Cables according to the present embodiments may also beconstructed to be low skew within the micromodules 20 so that they aresuitable for use in parallel optic transmission systems.

In one particular set of parameters, cables according to the presentembodiments may contain from four to twelve optical fibers within eachmicromodule 20. The dimensions of the micromodules 20 may be adjustedbased on the number of fibers within the module. The fibers 60 may beloosely disposed within the micromodules 20 in an essentially parallelarray. The fibers 60 may be coated with a thin film of powder, such aschalk or talc, which forms a separation layer that prevents the fibersfrom sticking to the molten sheath material during extrusion. The cable10 may be further encased in an interlocking armor for enhanced crushresistance.

The core 100 is illustrated as generally disposed in the center of thecable jacket 70, with the optical fibers 60 of the second group offibers 120 disposed around the periphery of the core tube 114. Thelocation of the strain-relief component 104, the optical fibers 60, andthe core 100 may vary, however, within the cable jacket 70 along thelength of the jacket. The core tube 114 may, for example, contact theinterior surface of the jacket 70 at one or more locations. One or moreof the optical fibers 60 in the second group 120 may also contact theexterior surface of the core tube 114 and/or the interior surface of thejacket 70 at one or more locations along the length of the cable 20.

The cable can be manufactured by first producing a core 100. The core100 can be manufactured by providing optical fibers 60 that willcomprise the first group of optical fibers 110 and extruding the coretube 114 about the first group of fibers 110. The core 100 is thenprovided along with the optical fibers 60 of the second group 120. Thecable jacket 70 is extruded over the fibers of the second group 120 andthe core 100. If present, the aramid fibers of the strength component104 are also provided within the cable jacket 70 during extrusion of thecable jacket.

FIG. 3 is a cross section a micromodule subunit cable 220 according to asecond embodiment and having a diameter 222. The micromodule subunit 220has a cable jacket 270 of thickness 272 that encloses a core 300. Astrain-relief component (not illustrated) may be disposed within aninterior 306 of the cable jacket 270 and surrounding the core 300. Thecable 220 may be similar in method of construction, materials ofconstruction, and dimensions as the cable 20 illustrated in FIG. 2.

As in the embodiment shown in FIG. 2, the optical fibers 260 arearranged in a first group 310 that are located within a core tube 314 ofthe core 300, and in a second group 320 that is located outside of thecore 300. The optical fibers 260 within the first group 310, which areenclosed within the core tube 314, are segregated and easilydistinguishable from those in the second group 320. In this exemplaryembodiment, the core 300 is disposed on one side of the interior 306,and the second group of fibers 320 is disposed on the other side.

According to one aspect of the present embodiments, the cables may havenonpreferential bend characteristics, of relatively small diameter, andutilize non-tight buffered fiber groupings. These features allow thecables to be easily attached to MTP connectors, and also allow for easyrouting of the fibers once in the MTP body.

Many modifications and other embodiments of the present invention,within the scope of the claims will be apparent to those skilled in theart. For instance, the concepts of the present invention can be usedwith any suitable fiber optic cable design and/or method of manufacture.For instance, the embodiments shown can include other suitable cablecomponents such as an armor layer, coupling elements, differentcross-sectional shapes, or the like. Thus, it is intended that thisinvention covers these modifications and embodiments as well those alsoapparent to those skilled in the art.

What is claimed is:
 1. A cable, comprising: a cable jacket; a corelocated within the cable jacket, the core comprising: a core tube; and afirst group of optical fibers disposed within the core tube; and asecond group of optical fibers disposed within the cable jacket andoutside of the core tube; and a strain-relief component disposed withinthe cable jacket and outside of the core tube; wherein the strain-reliefcomponent comprises a plurality of longitudinally extending tensileyarns; and wherein a diameter of the cable is 3.3 mm or less.
 2. Thecable of claim 1, wherein for each optical fiber in the first group, thecorresponding optical fiber in the second group has the same color andappearance thereof.
 3. The cable of claim 1, wherein at least one of theoptical fibers of the second group contacts an outer surface of the coreat at least one location.
 4. The cable of claim 1, wherein at least oneof the optical fibers of the second group contacts an inner surface ofthe cable jacket at at least one location.
 5. The cable of claim 1,wherein the first group of optical fibers comprises twelve opticalfibers and the second group of optical fibers comprises twelve opticalfibers.
 6. The cable of claim 5, wherein the twelve optical fibers inthe first and second groups have exterior coloring in the color sequenceof blue, orange, green, brown, slate, white, red, black, yellow, purple,rose, and aqua.
 7. The cable of claim 1, wherein the tensile yarnscontact the core tube and the cable jacket.
 8. The cable of claim 1,wherein the cable jacket comprises a PVC and the core tube comprises aPVC.
 9. A cable, comprising: a cable jacket; a core located within thecable jacket, the core comprising: a core tube; and a first group ofoptical fibers disposed within the core tube; and a second group ofoptical fibers disposed within the cable jacket and outside of the coretube; and a strain-relief component disposed within the cable jacket andoutside of the core tube; wherein the strain-relief component comprisesa plurality of longitudinally extending tensile yarns; and wherein adiameter of the cable is in the range of 2.0 mm to 5.0 mm.
 10. The cableof claim 9, wherein for each optical fiber in the first group, thecorresponding optical fiber in the second group has the same color andappearance thereof.
 11. The cable of claim 9, wherein at least one ofthe optical fibers of the second group contacts an outer surface of thecore at at least one location.
 12. The cable of claim 9, wherein atleast one of the optical fibers of the second group contacts an innersurface of the cable jacket at at least one location.
 13. The cable ofclaim 9, wherein the first group of optical fibers comprises twelveoptical fibers and the second group of optical fibers comprises twelveoptical fibers.
 14. The cable of claim 9, wherein the tensile yarnscontact the core tube and the cable jacket.
 15. The cable of claim 9,wherein the cable jacket comprises a PVC and the core tube comprises aPVC.
 16. A cable, comprising: a cable jacket; a core located within thecable jacket, the core comprising: a core tube; and a first group ofoptical fibers disposed within the core tube; and a second group ofoptical fibers disposed within the cable jacket and outside of the coretube, wherein a thickness of the cable jacket is in the range of 0.2 mmto 1.5 mm, a diameter of the core tube is in the range of 0.9 mm to 3.0mm, and a thickness of the core tube is in the range of 0.1 mm to 0.95mm.
 17. The cable of claim 16, further comprising an aramidstrain-relief component disposed within the cable jacket and outside ofthe core tube.
 18. The cable of claim 17, wherein at least one of theoptical fibers of the second group contacts an outer surface of the coreat at least one location and contacts an inner surface of the cablejacket at at least one location.
 19. The cable of claim 16, wherein eachoptical fiber in the first group has a corresponding optical fiber inthe second group of the same color and appearance.
 20. The cable ofclaim 16, wherein the cable jacket comprises a PVC and the core tubecomprises a PVC.